Conformational changes in the cytoplasmic domain of the Escherichia coli aspartate receptor upon adaptive methylation

By using targeted disulfide cross-linking, we have characterized structural changes that the Escherichia coli aspartate receptor undergoes upon modification of the four specific residues that are reversibly methylated during sensory adaptation. Cysteine residues were introduced at specific positions either in the cytoplasmic domain or in the periplasmic domain, and the rates of disulfide cross-linking were used to probe for conformational changes upon covalent modification. Conversion of the methylation sites from glutamates to glutamines greatly reduced the rate of disulfide formation between residues 265 and 265' and residues 250 and 250' in the cytoplasmic domain but not between residues 36 and 36' in the periplasmic domain. (Primes are used to indicate the second of the two identical subunits in the homologous dimer.) The covalent modification of the cytoplasmic domain induces conformational changes that are detectable in the cytoplasmic domain but none that are detectable in the periplasmic domain.